Revert of "Prevent race conditions between decrypt and close session"

[ Original CL http://ag/3890635,
  Merge of http://go/wvgerrit/50340 ]

The original fix was not sufficient to address all race conditions.
A subsequent CL will address them.

Bug: 73781703
Bug: 79158083
Bug: 79262108
Test: WV unit/integration tests, GTS GtsMediaTestCases tests and
      24 hours of continuous Netflix playback.

Change-Id: I869c22a250e2467b3d49935815e4157dc012fff5

libwvdrmengine/cdm/core/include/cdm_session.h

@@ -37,7 +37,7 @@ class CdmSession {
   CdmSession(FileSystem* file_system, metrics::SessionMetrics* metrics);
   virtual ~CdmSession();
 
-  void Close();
+  void Close() { closed_ = true; }
   bool IsClosed() { return closed_; }
 
   // Initializes this instance of CdmSession with the given property set.
@@ -263,9 +263,6 @@ class CdmSession {
   bool mock_license_parser_in_use_;
   bool mock_policy_engine_in_use_;
 
-  // Lock to avoid race conditions between Close() and Decrypt()
-  Lock close_lock_;
-
   CORE_DISALLOW_COPY_AND_ASSIGN(CdmSession);
 };
 

libwvdrmengine/cdm/core/include/wv_cdm_types.h

@@ -333,7 +333,6 @@ enum CdmResponseType {
   GET_PROVISIONING_METHOD_ERROR = 289,
   SESSION_NOT_FOUND_17 = 290,
   SESSION_NOT_FOUND_18 = 291,
-  SESSION_CLOSED_1 = 292,
 };
 
 enum CdmKeyStatus {